Geroter gear sets commonly used in hydraulic motors and pumps are expensive to design and difficult to manufacture to the necessary close tolerances. Special cutters must be provided for machining the teeth. The sliding of one gear against the other causes wear, eventually destroying the fluid-tight contact between the mating gear faces and requiring one or both of the gears to be replaced at considerable expense.
Others have modified 2-member internal gear sets by replacing the teeth of the outer gear member with rollers which may be positioned in oversize recesses as in U.S. Pat. No. 3,591,320 (Woodling). That patent does not suggest any change in the inner gear member which, as illustrated, has a geroter tooth form. U.S. Pat. Nos. 3,289,602 (Hudgens) and No. 3,627,454 (Goff) similarly show hydraulic devices wherein a conventional inner geroter gear member cooperates with an outer gear member comprising rollers retained in recesses.
While no prior art has been found showing a 3-member geroter or other internal ger set employing rollers, the teachings of the aforementioned patents should be applicable to such 3-member gear sets, namely, that the inner-facing teeth may be replaced by rollers.